Several examples can be found in which curable mixtures are used to produce inkjet recording media. EP-A-1 289 767, EP-A-1 418 058 and EP-A-1 477 318 disclose layers, cured by UV or other radiation in which the porous character is provided by organic or inorganic particles in order to obtain sufficient solvent uptake. However, application of inorganic particles can cause physical weakness of the layer, resulting in cracking or breaking of the layer.
EP-A-0 738 608 describes curing compositions containing a water soluble high-molecular weight compound, but these compositions yield solid layers and therefore do not dry quickly.
WO-A-99/21723 discloses a substrate coated with a binder dissolved in an aqueous solvent mixture, which layer is then cured, and teaches that any amount of solvent is suitable, and there is no limit to the degree in which the binder is diluted before curing.
WO-A-01/91999 and GB-A-2 182 046 disclose a curable inkjet coating that is cured after drying the coating.
U.S. Pat. No. 6,210,808 describes an inkjet recording sheet wherein a colloidal suspension of water-insoluble particles and water-insoluble monomers/prepolymers is cured.
U.S. Pat. No. 6,734,514 discloses a radiation curable coating for ink jet printing comprising water insoluble latexes.
Another method is the application of foamed layers as in for example EP-A-0 888 903.
In the above mentioned prior art the receiving layer is not isolated, but formed directly on the substrate after drying and/or further manipulation of the coated substrate. It would be advantageous, to be able to isolate such a layer as a membrane which can be used as such or which can be applied to a substrate in a separate process to give advantageous properties, for instance as an inkjet receiving medium. Membranes are produced by various methods such as dry and wet phase inversion of polymeric solutions, stretching of homogeneous, partially crystalline polymer films, sintering of particulate materials, thermal gelation of homogeneous polymer solutions and by radical polymerization with simultaneous phase separation by irradiation or thermal initiation. Of these methods the wet phase inversion method—in which a polymer solution is contacted with a precipitating agent or non-solvent causing separation into a solid polymer-rich phase and a liquid solvent-rich phase—is by far the most widely used technique for obtaining porous structures. Examples in which this technique is applied can be found in WO-A-98/32541, WO-A-2005/016655, U.S. Pat. No. 4,707,265, U.S. Pat. No. 6,079,272, EP-A-0 803 533, EP-A-0 812 697, EP-A-0 824 959, EP-A-0 889 080 and EP-A-1 149 624.
The main disadvantages of wet phase inversion are the limited production speed obtainable and the high amounts of organic solvents required.
Dry phase inversion processes are described e.g. in EP-A-1 176 030. An alternative method is disclosed in U.S. Pat. No. 4,466,931, EP-A-0 216 622 and EP-A-0 481 517 describing a membrane which is produced by irradiating curable monomers in non-volatile organic solvents which are to be removed by washing with a washing liquid of low boiling point.
As many curable compounds are hydrophobic in nature both dry and wet phase inversion techniques require organic apolar solvents to obtain a clear solution. Since these membranes are often not hydrophilic an additional process step may be required to make the membrane hydrophilic for instance by impregnating the membrane with a saline solution as is described in e.g. FR-A-2 687 589, with molecules that comprise hydrophilic and hydrophobic groups as is described in e.g. WO2004/022201 or with a solution of a cationic or anionic polymer as is described in e.g. JP-A-2 107 649.
Membranes can also be made by other methods such as thermal polymerization as described in e.g. EP-A-0 251 511, JP-A-5 177 120 and U.S. Pat. No. 4,942,204 or grafting acrylic acid to PVC films as described in GB-A-1 549 352 but these membranes or films are not porous and are not formed by phase separation from a solvent.
Membranes made from amphiphilic copolymers as free standing films are described in WO-A-01/88025 which are also not porous and of relatively small size (up to 1 mm2).
Although under certain conditions acceptable results can be obtained with the above-mentioned prior art materials, there is still a need for improvement. The present invention seeks to fulfill, at least in part, this need.
For recording media improvement is required in particular with respect to smearing properties, which may be associated with absorption properties of the porous film, in particular absorption speed. At the same time a porous film must be provided that has a good gloss.
There is a need for a membrane that can be produced at high speeds without requiring costly measures to guarantee safety and to prevent pollution of the environment. This invention aims at solving these problems, at least in part.